Cutting fluids are used with abrasive materials, e.g., silicon carbide (SiC), to form cutting slurries at a weight ratio typically between 0.5 and 1.5, commonly about 1. This slurry is sprayed on the cutting tool, e.g., a wire saw, to cut a brittle work piece, e.g., a silicon ingot. For optimum performance of the cutting fluid, the abrasive material needs to be evenly suspended and dispersed throughout the fluid, and this requires that the fluid have a certain viscosity to prevent Brownian movement of abrasive materials.
Non-aqueous cutting fluids e.g., those based on a PAG like polyethylene glycol (PEG), are popular in the current market. However, abrasive materials like SiC are not well dispersed in this kind of medium. Wafer producers need to agitate the slurry constantly. On the other hand, good cooling is also required to reduce the thermal stress on the wafer and to avoid swelling of various components of the wire saw apparatus, e.g., the cutting wires, the jig that holds and guides the wafer, etc.
Water has good cooling efficiency and has been tried both as the main dispersing medium of a cutting fluid, and as a component in a cutting fluid blend of water and a PAG. However, the addition of water to a cutting fluid comprising PAG dramatically reduces the viscosity of the fluid and thus not only detracts from the suspension and dispersion properties of the PAG, but also allows for the abrasive materials to settle out of suspension.
The addition of a second dispersing agent can assist in the suspension and dispersion of the abrasive material. U.S. Pat. No. 6,673,754 teaches polycarboxylic acid as such a dispersing agent. The problem, however, is that this kind of conventional polycarboxylic acid has poor compatibility with conventional cutting fluid materials like PEG. Of interest to the manufacturers and users of cutting fluid is a method of improving the suspension and dispersion of abrasive materials in a cutting fluid.